RewriteEngine On
Redirect to www
RewriteCond %{HTTP_HOST} ^domain.com$ [NC]
RewriteRule ^(.*)$ http://www.domain.com/$1 [R=301,L]
Redirect to non-www
RewriteCond %{HTTP_HOST} ^www.domain.com$ [NC]
RewriteRule ^(.*)$ http://domain.com/$1 [R=301,L]
Where 'domain.com' is your actual domain name
